A medical ultrasonic diagnostic apparatus and an ultrasonic image examination apparatus transmit ultrasonic waves to an object via an ultrasonic probe and visualize the inside of the object based on the reflection signal (echo signal) generated by reflected waves from the inside of the object. The medical ultrasonic diagnostic apparatus and the ultrasonic image examination apparatus mainly use an electronic operation type array ultrasonic probe having an ultrasonic transmission/reception function.
A general ultrasonic probe includes a backing member, piezoelectric transducers joined on the backing member and having electrodes formed on the two surfaces of the piezoelectric bodies, and acoustic matching layers joined on the piezoelectric transducers. The piezoelectric transducers and the acoustic matching layers are formed as a plurality of channels by array processing. An acoustic lens is formed on the acoustic matching layers. The electrodes of the piezoelectric transducers corresponding to the respective channels are connected to the apparatus main bodies of the medical ultrasonic diagnostic apparatus and ultrasonic image examination apparatus via a control signal board (flexible printed circuit [FPC] board) and cables.
In such an ultrasonic probe, the piezoelectric transducers are active components which transmit and receive ultrasonic waves. Each piezoelectric transducer is required to have the characteristics of being large in dielectric constant and piezoelectric constant and small in dielectric loss.
As a material for each piezoelectric transducer, PZT (lead zirconate titanate)-based piezoelectric ceramic has been used since 1970s. As a material for each piezoelectric transducer, a high-performance piezoelectric single crystal having a lead complex perovskite structure has begun to be used since about 2005. A high-performance piezoelectric single crystal having a lead complex perovskite structure is formed from a piezoelectric single crystal containing a relaxor-based lead complex perovskite compound comprising lead titanate (PbTiO3) and Pb(B1, Nb)O3 (wherein B1 is at least one of magnesium, zinc, indium, and scandium).
The related art discloses a piezoelectric single crystal which is a pseudo-cubic crystal phase single crystal having a lead complex perovskite structure with the composition [Pb(Mg, Nb)O3](1-x).[Pb(TiO3)](x) (to be referred to as PMN-PT hereinafter): (x=0.26 or more to 0.29 or less) or the like, and whose dielectric constant at 25° C. is 5,000 or more and specific dielectric constant at a transformation temperature Trt between a pseudo-cubic crystal phase and a tetragonal crystal phase is 2.5 times or more the specific dielectric constant at 25° C.
Another related art discloses that it is possible to control the domain size of lead zinc niobate-lead titanate Pb(Zn1/3, Nb2/3)O3—Pb(TiO3) (to be referred to as PZN-PT hereinafter) in the range of 8 to 20 μm in accordance with conditions by applying a DC electric field while lowering a high temperature equal to or higher than the phase transition temperature. The domain in this method is formed in a direction parallel to the electrode surface.